1. Field of the Invention
The present invention relates to a method of producing a polymerized toner for developing a latent image of electrostatics (hereinafter, it may be simply referred as “a toner”) used for development of a latent image of electrostatics in an electrophotography, an electrostatic recording method, an electrostatic printing process or the like. Particularly, the present invention relates to a method of producing a polymerized toner which is small in an amount of a microparticle produced as a by-product and an amount of a polymerizable monomer remained and is excellent in printing durability.
2. Description of the Related Art
An electrophotography is a method of obtaining a printed product in such a manner that a latent image of electrostatics formed on a photosensitive member is developed by a toner comprising a colored polymer particle, and if required, other particles such as an external additive, a carrier, or the like, the toner is transferred to a transferring material such as paper, an OHP sheet or the like, and the transferred toner is fixed on the transferring material. As a method of development using a toner or a method of fixing a printed image of a toner, conventionally various kinds of methods has been proposed. A method suitable for requirement of forming an image is selected.
Recently, the need of colorization for image-forming devices such as copying machines, facsimiles printers or the like is increasing. Since in color printing, an image requiring high resolution and reproduction of a clear color tone such as a photograph or the like is also printed, a colored toner which can suffice such requirements is needed.
As for the toner, various properties are required such as environmental stability from the viewpoint of preventing deterioration of an image quality due to environmental changes such as temperature, humidity or the like, printing durability (property to be able to endure continuous printing, that is, property that problems such as filming, generation of vertical stripes, generation of fog and the like do not occur to a printing device, a printed product or the like when printing is performed continuously) from the viewpoint of reduction in toner consumption, low-temperature fixing ability from the viewpoint of reduction of an electric power consumption, or the like.
In order to increase resolution of a printed product to be obtained, since both excellent transferability and dot reproducibility can be attained, a spherical toner having a small particle diameter is suitable. As a method of producing such a toner, a polymerization method is proposed.
In a conventional pulverization method, particularly, when a toner having a small particle diameter is produced, yield decreases and much energy is consumed for pulverization. To the contrary, a polymerization method is high in yield, consumption energy is low as the pulverization process is not required, and further a spherical toner can be easily produced.
Among the methods for producing a toner (a polymerized toner) by the polymerization method, a suspension polymerization method is widely utilized. In the suspension polymerization method, firstly, a polymerizable monomer, a colorant, a charge control resin, and if required, other additives are mixed to prepare a polymerizable monomer composition, and the polymerizable monomer composition is dispersed in an aqueous medium containing a dispersion stabilizer. Next, high shear is applied to the aqueous medium having the polymerizable monomer composition dispersed by means of a high-speed agitator or the like to form a droplet of the polymerizable monomer composition. Then, the aqueous medium having the polymerizable monomer composition dispersed and having the droplet formed is polymerized in the presence of a polymerization initiator followed by filtration using a filter, washing and drying, thus, a colored polymer particle is obtained. Further, the colored polymer particle is mixed, if required, with a carrier and/or an external additive such as an inorganic microparticle or the like to obtain a polymerized toner.
It is a problem of the method of producing the polymerized toner that a microparticle having a submicron order particle diameter is produced as a by-product upon polymerization to obtain the colored polymer particle besides a desired colored polymer particle (hereinafter, the microparticle produced as a by-product may be referred as “a by-product microparticle”). If the microparticle is produced as a by-product, a part of the microparticles released clogs the filter upon filtration of the obtained colored polymer particle from the aqueous medium. Hence, a filtration rate decreases.
Also, if a polymerized toner is produced from the colored polymer particle containing a lot of by-product microparticles and the polymerized toner is used for printing, the by-product microparticle is likely to adhere to members in a developer since the by-product microparticle is significantly small in particle diameter and thereby has high adherence. When plural prints are printed using the polymerized toner, the attached by-product microparticle is gradually accumulated so as to cause filming (adherence) to the member. When the by-product microparticle causes filming on a developing blade or a sealing member between a developing roll and a toner container, an even toner layer cannot be formed on the developing roll so that vertical stripes are likely to be generated on an image. If filming is caused on the developing roll or the photosensitive member, a fog is generated on a transferring material such as paper or the like to cause decrease in durability of the toner. Hence, development of a method to inhibit production of such a microparticle as a by-product is desired.
In order to satisfy such various demands of properties including the environmental stability, the printing durability, the low-temperature fixing ability and so on, and the prevention of microparticle produced as a by-product, further insights are provided into a method of forming an image and a toner used therefore.
Firstly, WO2002/077717 can be exemplified. WO2002/077717 discloses a method of producing a toner, in which a polymerizable monomer composition containing a polymerizable monomer and a colorant is polymerized in an aqueous medium in the presence of a compound “A” selected from the group consisting of (1) a thiazole thio compound , (2) a thiuram compound (particularly, thiuram disulfide) and (3) a dithio carbamate compound, proposed for the purpose of stable production of a toner which is excellent in a balance between fixing ability and shelf stability and can form a clear image, particularly in the case of a colored toner, for the purpose of production of a toner excellent in a sharp melt property required for reproduction of a clear color tone of a color image. However, the prevention of microparticle as a by-product is not taken into account in WO2002/077717 and the method is insufficient in the effect of inhibiting production of a microparticle as a by-product according to the result of research done by the inventor of the present invention (not disclosed). Also, the amount of polymerizable monomer remained in the toner is large.
Next, as a method to inhibit production of the microparticle as a by-product, a method of producing a toner using a specific azo compound as a polymerization initiator and a hydroquinone based compound as a polymerization inhibitor is proposed (Japanese Patent Application Laid-Open (JP-A) No. 2004-302239). However, the method is insufficient in the effect of inhibiting production of the microparticle as a by-product.
Also, a method to produce a toner, in which a polymerizable monomer composition containing a radical polymerizable monomer as a polymerizable monomer, a colorant and a radical polymerization inhibitor soluble to the radical polymerizable monomer and soluble to an alkali aqueous medium as other additive is suspended in an alkali aqueous medium followed by polymerization, is proposed (JP-A No. 5-100484). However, the method is insufficient in the effect to inhibit production of the microparticle as a by-product. Even further, the durability of the toner is inferior. Furthermore, there is a problem of generation of an odor upon printing due to the polymerizable monomer such as styrene, a decomposed product of a polymerization initiator or the like remained in the toner. If there is a large amount of the polymerizable monomer or the like remained in the toner, a component such as a wax or the like present in the toner may exude on the surface of the toner during storage besides the problem of the odor. It causes a problem that aggregation of the toner further increases and filming to a photosensitive member or the like is more likely to be generated.
An object of the present invention is to provide a method of producing a polymerized toner which is small in an amount of a microparticle produced as a by-product and an amount of a polymerizable monomer remained, generates no filming upon printing and is excellent in printing durability.